Is declining a draw when losing but opponent is low on time bad etiquette?

I encountered this situation in a live tournament game today. My opponent was a pawn up in the endgame. The game was very unclear and thought it was probably a draw at worst and maybe I still had winning chances. My opponent was playing very slow, and he let his time click down to under a minute before offering me a draw. I was almost certain that I would win on time, so I declined and won quickly after.

I didn't see anything wrong with it, but it felt really weird getting the extra half point that way. 

no. Time management is part of timed games.  You can say your opponent might have had more of an advantage taking longer to think his moves out that you did moving faster.

He was only up a pawn?  Hardly a big deal. 

The sweetest win of all is when you are losing horrifically and win on time.  

from 690 to 790 elo thats pretty much what i did

I see no problem, the clock is part of the game. 

No. they were probably also trying it on by offering a you a draw when it became apparent they was going to lose on time.

You shouldn't feel bad at all, just another type of win.